Setup VPN on Mac Mini Server running OSX through a BT Hub Router

Question

Hello everyone,
I know this question has been posted several times and I have looked at the suggested solutions, trying each of them. I think this is really down to my lack of knowledge hence hoping someone out there could point me to the right direction for more resources / information, please.
I am trying to setup a Mac Mini Server with VPN access. My server sits behind a BT Hub router. These are the steps that I have been through:
1. I am using the server app and after registering a free account with no-ip, I got myself a host name <myname>.ddns.net.
2. Then I setup the server using a domain name
3. I configured the DNS by first setting up a primary zone - zone: ddns.net. Then added machine record host name: <myname> pointing to my server which I have configured my router to assign a static ip address to it at 192.168.x.x
4. Then, I configured the VPN setting up for L2TP and PPTP, setup the shared secret, change the ip address range to match that of the DHCP range on my router. My router by default has a DHCP range between 64 - 253.
5. Then, I also configured my router to port forward 500, 1701, 1723, and 4500 to my server at 192.168.x.x (I selected both TCP and UDP).
6. Finally, setup a user account with account name test and password abcd12345
7. Gone on my "client" machine which is basically my Samsung S4 handphone, selected VPN -> PPTP -> server address: <myname>.ddns.net -> entered account name test and password abcd12345.
This didn't work.
Then, I read some post about manually configure DHCP on the server app. Went on the server app, turned on DHCP and setup a network named TestDHCP. Assigned ip address range between that of the default DHCP range on my BT Hub router.
This does not work either.
Could someone please kindly help me with it? I am completely lost.
Thank you in advance.

Answer 1

To run a public VPN server behind an NAT gateway, you need to do the following:
1. Give the gateway either a static external address or a dynamic DNS name. The latter must be a DNS record on a public DNS registrar, not on the server itself. Also in the latter case, you must run a background process to keep the DNS record up to date when your IP address changes.
2. Give the VPN server a static address on the local network, and a hostname that is not in the top-level domain "local" (which is reserved for Bonjour.)
3. Forward external UDP ports 500, 1701, and 4500 (for L2TP) and TCP port 1723 (for PPTP) to the corresponding ports on the VPN server.
If your router is an Apple device, select the Network tab in AirPort Utility and click Network Options. In the sheet that opens, check the box marked
          Allow incoming IPSec authentication
if it's not already checked, and save the change.
With a third-party router, there may be a similar setting.
4. Configure any firewall in use to pass this traffic.
5. Each client must have an address on a netblock that doesn't overlap the one assigned by the VPN endpoint. For example, if the endpoint assigns addresses in the 10.0.0.0/24 range, and the client has an address on a local network in the 10.0.1.0/24 range, that's OK, but if the local network is 10.0.1.0/16, there will be a conflict. To lessen the chance of such conflicts, it's best to assign addresses in a random sub-block of 10.0.0.0./0 with a 24-bit netmask.
6. "Back to My Mac" is incompatible with the VPN service. It must be disabled both on the server and on an AirPort router, if applicable.
If the server is directly connected to the Internet, see this blog post.